RFID protocol for improved tag-reader communications integrity

Abstract

The present invention provides a means by which the reliability of communication between any RFID reader and tag in an RFID system is improved by using an “interleaved parity” algorithm. The improved reliability is obtained by computing, on one RFID device, an interleaved parity code for a message, sending the message with the code from the RFID device, receiving the message on the other RFID device which computes another interleaved parity code for the received message. The two parity codes are compared and if the codes are the same, the message can be parsed and interpreted. If the codes indicate that one bit of the message is incorrect, the incorrect bit is corrected and the message is parsed and interpreted. Otherwise, a request for a new message is sent to the RFID device, and, if appropriate, an indication of two erroneous bits is also sent.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates to the field of radio frequency identification (RFID) and, more particularly, to improved reliability of communication between any RFID reader and tag in an RFID system.[0003]2. Discussion of the Prior Art[0004]RFID systems exhibit unique communications reliability issues. Communication in RFID systems is normally initiated by the transmission of a carrier signal from the reader to the tag. However, this communication could also be from the tag to the reader. Reliability issues arise due to the relatively high instability of the RF field strength, the relatively error-prone decoding of received signals at both the reader and tag, and the uncertainty in the timing of the carrier detection. RF field strength may become insufficient and / or may fluctuate frequently. The RF field strength instability is evidenced, for example, if the carrier signal amplitude or quality is degraded by, for instance, mov...

AI Technical Summary

Benefits of technology

[0009]The present invention advantageously provides a means by which the reliability of communication between any RFID reader and tag in an RFID system can be improved by the use of an “interleaved parity” algorithm to solve the above problems in the prior art. The improved reliability of communication can be obtained by computing, on either the RFID reader or RFID tag, an interleaved parity code for a message, sending the message with the code from the RFID device, receiving the message on the other RFID device wherein another interleaved parity code is computed for the received message. The two parity codes are compared to each other. If the codes are the same, the sent message is the same as the received message, which can then be parsed and interpreted. If the codes indicate that one bit of the message is incorrect, the incorrect bit is corrected and the message is parsed and interpreted. If the comparison indicates that an error has occurred in two bits of the message, a request for a new message along with an indication of the erroneous two bits is sent to the RFID device. If the comparison indicates that more than two bits have errors, a new message is requested from the RFID device.

Problems solved by technology

RFID systems exhibit unique communications reliability issues.

Reliability issues arise due to the relatively high instability of the RF field strength, the relatively error-prone decoding of received signals at both the reader and tag, and the uncertainty in the timing of the carrier detection.

RF field strength may become insufficient and / or may fluctuate frequently.

The RF field strength instability is evidenced, for example, if the carrier signal amplitude or quality is degraded by, for instance, movement of the reader relative to the tag.

Degraded carrier signal quality can cause the integrity of the transaction to be lost, resulting in an incorrectly received message and, if the error is detected, necessitating retransmission of the entire transaction or message.

In addition, it is common for RFID systems to be operated close to the limits of their range, so that even in the absence of movement, the RF field strength may vary, causing a high bit error rate of the receiving device, either the reader or the tag.

Another communications reliability issue arises due to the uncertainty in the timing of carrier detection relative to the start of reading or transmission.

This uncertainty can give rise to a shifting, or partial shifting, of a carrier or message acknowledgement bit stream, and can cause the failure of standard message parsers, which may not be equipped to handle this shifting bit stream.

In passive tags, where the carrier also supplies energy and / or a signal path for the response of the tag, this shifting can be acute, resulting not only in misinterpretation of the reader's request, but also in an inappropriate response by the tag, causing a two-way communications failure.

In active tags, the communication requests between the reader and the tag may be more complex, requiring specific tasks for the reader to validate the results received from the tag and for the tag to validate requests from the reader.

These techniques frequently result in high energy consumption at the reader, often limiting the use of portable readers, and also in RF interference of the RFID system when its signal is injected into receivers, e.g., intermediate stage receivers, for other RF systems in a location.

All of these methods reduce throughput and may require manual intervention by the user in order to achieve reliable transmission.

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